This invention relates to a control for a grating assembly of the type where a movable grating moves between OPEN and CLOSED positions relative to a fixed grating.
The OPEN position is the position where there is the largest alignment of the passages through the stationary and moving gratings within the range of movement of the movable grating. The CLOSED position is that where the movable grating fills the largest extent, within its range of movement of the passages, through the fixed grating.
In applicant's prior patents U.S. Pat. Nos. 6,340,329 and 6,744,559 there is described a temperature sensing control system wherein in the cold months the control system controls the temperature in the space fed by air flow through the grating by moving the movable grating to OPEN position to increase heat flow into the space and to CLOSED position to decrease heat flow into the space. (As the patents explain in warm weather the control system may preferably be connected to move the grating to OPEN and CLOSED positions to decrease and increase heat respectively.)
In the movable grating drive described in the patents a drive means drove the movable grating between OPEN and CLOSED positions through a yieldable drive. This drive embodied the sought for advantage that when the movable grating moved toward CLOSED position, if it met an object, then the yieldable connection allowed travel of the movable grating toward the CLOSED position to stop, (even though the drive means continued to move) to prevent damage to the object or the control system. There were not felt to be comparable advantages from the use of the yieldable drive when the grating moved toward the OPEN position.
The drive worked very well, however two disadvantages were encountered. Firstly, some considerable difficulty was encountered in installing the springs for the yieldable drive. Secondly, the drive thus constituted caused some noise. Although this noise was insignificant enough to be almost undetectable during the day, at night in an otherwise silent environment the noise of the drive could be sufficiently audible to be annoying.